We propose to continue studies designed to determine if osteogenic phenotypes arise in vitro from undifferentiated limb (chick) mesenchymal cells. Studies at the electron microscopic level, analyzing the adenylate cyclase system, analyzing the collagen and analyzing various biochemical parameters are to continue and will hopefully provide support for our preliminary observations with regard to the identification of osteogenic phenotypes in cultures of undifferentiated mesenchymal cells. Preliminary evidence analyzing the above parameters seems to strongly indicate that bone formation (including the appearance of calcium apatite) does, indeed, take place under defined culture conditions. Future experimentation is designed to exploit this experimentally advantageous system.